From patchwork Wed Jun 1 21:09:46 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Axel Rasmussen X-Patchwork-Id: 12867284 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 43720C43334 for ; Wed, 1 Jun 2022 21:10:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231359AbiFAVK2 (ORCPT ); Wed, 1 Jun 2022 17:10:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54296 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231219AbiFAVJ7 (ORCPT ); Wed, 1 Jun 2022 17:09:59 -0400 Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0EEF1396B8 for ; Wed, 1 Jun 2022 14:09:58 -0700 (PDT) Received: by mail-yb1-xb49.google.com with SMTP id 84-20020a250557000000b0065bb92955a2so2468225ybf.1 for ; Wed, 01 Jun 2022 14:09:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=kk1kl2p/g3Lg3sGUGGyiVv3dYTdsKPpPMBPxg1a8NQs=; b=fCqYWeX5V2UAR6CwDd1WwVkx3nRbWoxq+i5xyuQYRpLuf0Idp6IKcChFZX/d1mGPZa wZJhNzo1ICxiw03yrG17zNvxeU/gt4XldskATEVn3qYus+EBAdrY62rsfcD40sYP7ZrX igXgB45R6xlblsq1J3+7HLWq0D7FHjeEccdGgPATYEG27fmiy5xS6olETvuNNrcqmkET CeeuEs1LWViL+Kl2RWA6FUcmNKliAcGPMy3chE3EZPK2ANXrTqk3lk3J9/9XTb5021lB diS31DsFxp7coKuQWeAxr68utYOwsJ9ksZ4/IluHlLeghUUS59fRs6MgqNyQ+1D8i2L/ j7tA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=kk1kl2p/g3Lg3sGUGGyiVv3dYTdsKPpPMBPxg1a8NQs=; b=PzEx4Vh22f5GyD3kAHF9QEJNOuHEngoY0pYF9qbcnTTN6TtclJfVLmXQuegsS3M25R xKugbWPncdceLgMc06iowEd7erZ5pOMwgmSz2JUbThXd2XUuUw0sEjNatgsu0X3XGVS5 OWJfjCXFlitozDvqEzbNRtw2cKOOr7T2pszDc80edL+AxbzDrat8X7JCeHihku8NKzKC w0jPW8P1x8g9mInXILAzCHLbuJLJR1YgsGoYD1JiT4vVoobNSrgrofHq6lqSyj8dKGPt Crt/P601udXq7Tv3t7iECFhM55yGv3bm8WaCLKsR2pFGAmb0GSXAtTacc36EsLoIlyVB BOWg== X-Gm-Message-State: AOAM532es6N7fhsZrpgHs0j24/l5iarQKASxqnhxGqw3V79FaPjGE40Q cjmvuD9V2hQGCCWt7B/DfHb02Ptq9OTMXlcOdhJ/ X-Google-Smtp-Source: ABdhPJy7KiJc6d2+d7s0OkiwmpYfryNL4lT4rDOmPy5rS9SoXCCHdlUkPE20eNU2mwq5x8ofn4egdPxMllMcAtmZ8mur X-Received: from ajr0.svl.corp.google.com ([2620:15c:2cd:203:aaec:e358:9f0e:2b26]) (user=axelrasmussen job=sendgmr) by 2002:a81:47d4:0:b0:2ff:c3d1:c158 with SMTP id u203-20020a8147d4000000b002ffc3d1c158mr1702500ywa.388.1654117797191; Wed, 01 Jun 2022 14:09:57 -0700 (PDT) Date: Wed, 1 Jun 2022 14:09:46 -0700 In-Reply-To: <20220601210951.3916598-1-axelrasmussen@google.com> Message-Id: <20220601210951.3916598-2-axelrasmussen@google.com> Mime-Version: 1.0 References: <20220601210951.3916598-1-axelrasmussen@google.com> X-Mailer: git-send-email 2.36.1.255.ge46751e96f-goog Subject: [PATCH v3 1/6] selftests: vm: add hugetlb_shared userfaultfd test to run_vmtests.sh From: Axel Rasmussen To: Alexander Viro , Andrew Morton , Charan Teja Reddy , Dave Hansen , "Dmitry V . Levin" , Gleb Fotengauer-Malinovskiy , Hugh Dickins , Jan Kara , Jonathan Corbet , Mel Gorman , Mike Kravetz , Mike Rapoport , Nadav Amit , Peter Xu , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , zhangyi Cc: Axel Rasmussen , linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, Shuah Khan Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org This not being included was just a simple oversight. There are certain features (like minor fault support) which are only enabled on shared mappings, so without including hugetlb_shared we actually lose a significant amount of test coverage. Reviewed-by: Shuah Khan Reviewed-by: Peter Xu Signed-off-by: Axel Rasmussen --- tools/testing/selftests/vm/run_vmtests.sh | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/tools/testing/selftests/vm/run_vmtests.sh b/tools/testing/selftests/vm/run_vmtests.sh index 54a0c28f810c..7e102246dd9f 100755 --- a/tools/testing/selftests/vm/run_vmtests.sh +++ b/tools/testing/selftests/vm/run_vmtests.sh @@ -121,9 +121,11 @@ run_test ./gup_test -a run_test ./gup_test -ct -F 0x1 0 19 0x1000 run_test ./userfaultfd anon 20 16 -# Test requires source and destination huge pages. Size of source -# (half_ufd_size_MB) is passed as argument to test. +# Hugetlb tests require source and destination huge pages. Pass in half the +# size ($half_ufd_size_MB), which is used for *each*. run_test ./userfaultfd hugetlb "$half_ufd_size_MB" 32 +run_test ./userfaultfd hugetlb_shared "$half_ufd_size_MB" 32 "$mnt"/uffd-test +rm -f "$mnt"/uffd-test run_test ./userfaultfd shmem 20 16 #cleanup From patchwork Wed Jun 1 21:09:47 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Axel Rasmussen X-Patchwork-Id: 12867278 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 73613C433EF for ; Wed, 1 Jun 2022 21:10:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231201AbiFAVKV (ORCPT ); Wed, 1 Jun 2022 17:10:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54464 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231254AbiFAVKB (ORCPT ); Wed, 1 Jun 2022 17:10:01 -0400 Received: from mail-yw1-x114a.google.com (mail-yw1-x114a.google.com [IPv6:2607:f8b0:4864:20::114a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 425D537A18 for ; Wed, 1 Jun 2022 14:10:00 -0700 (PDT) Received: by mail-yw1-x114a.google.com with SMTP id 00721157ae682-3077947cbb8so25837297b3.8 for ; Wed, 01 Jun 2022 14:10:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=901BpGHrP+WIymgStsREu89QnSrikR1eEvI9Dywbhsg=; b=BDJQcZ3k6VMLBGyDFzZskGuhBtnhdv42pQSckQsLOWCyVY7Xqf+2kT63J4F/d4bERE eydSs350ZLrk9nUqPl9uN8eOgJ01RknjccM4Di1YTbAf9nU4OlzFg7cxyxjYQ5EKFWXr hSQZYI/wunCARCD3fV8pt2KU6p/TGSGgBqHFrFpAyh3tcUXRhX73g6MT4b/9yRUbKN4d Yab5MzaGyeDAbdQugNMawgPRymIxc7tEcm+P8nS8wWhvmL/iUv/XqZ+RzapypeyousAZ T3evxkBkhGTICfx4jRI64IFNbHtW8RkuJv9zbUpafjqZyn8P8WygujdsYUelbZVUYBtU f4Zg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=901BpGHrP+WIymgStsREu89QnSrikR1eEvI9Dywbhsg=; b=TlRrVpIgepi3yi8+6QUehDHfziXOPXesa9e59sAFcEXenV86ul+Ia1iCvhjuJyuQlI FoMaLwf1AQz/DAprTS66DikmX+IPTf5Y+5XCkzGBitB1pOmRJtTBqAq3U2AesUpdJPW3 8hdLE/YFshNzgmvBGEWVT9TWOVsEKqGAKx6/QqDdQn2GRCR4jolsaLp54w2o5sRtmJsj DtC+6twOCERKnmTDTRKfzq2nScNk4inRtZveLKlM83SxbLw96kSxOIq99hhy9VliexSm MEOjYKxBeP37QqEj+Dsb37OZOb5Sg8cdBstQYlGM3xql6nwRjBoZb0SH2gUPwdkvOqTu fBYQ== X-Gm-Message-State: AOAM532IX88rNav0SW78KZKxRA4ThEtEuK0RjGWusyw+la+KACwrdFDW RfQIcJrnGzRyBHerxPp5U/7wWxZpZpXiCS4JIhtY X-Google-Smtp-Source: ABdhPJw5CfsqBtuSRUvpx1MwggnCJckvoUqHXGCXU20XJb4bXPK6ug8yRK0rKKD/5bVEMCBJoJnLvnmpm2vCkd8dTOYp X-Received: from ajr0.svl.corp.google.com ([2620:15c:2cd:203:aaec:e358:9f0e:2b26]) (user=axelrasmussen job=sendgmr) by 2002:a0d:d003:0:b0:2eb:6441:d9a3 with SMTP id s3-20020a0dd003000000b002eb6441d9a3mr1669520ywd.273.1654117799431; Wed, 01 Jun 2022 14:09:59 -0700 (PDT) Date: Wed, 1 Jun 2022 14:09:47 -0700 In-Reply-To: <20220601210951.3916598-1-axelrasmussen@google.com> Message-Id: <20220601210951.3916598-3-axelrasmussen@google.com> Mime-Version: 1.0 References: <20220601210951.3916598-1-axelrasmussen@google.com> X-Mailer: git-send-email 2.36.1.255.ge46751e96f-goog Subject: [PATCH v3 2/6] userfaultfd: add /dev/userfaultfd for fine grained access control From: Axel Rasmussen To: Alexander Viro , Andrew Morton , Charan Teja Reddy , Dave Hansen , "Dmitry V . Levin" , Gleb Fotengauer-Malinovskiy , Hugh Dickins , Jan Kara , Jonathan Corbet , Mel Gorman , Mike Kravetz , Mike Rapoport , Nadav Amit , Peter Xu , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , zhangyi Cc: Axel Rasmussen , linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org Historically, it has been shown that intercepting kernel faults with userfaultfd (thereby forcing the kernel to wait for an arbitrary amount of time) can be exploited, or at least can make some kinds of exploits easier. So, in 37cd0575b8 "userfaultfd: add UFFD_USER_MODE_ONLY" we changed things so, in order for kernel faults to be handled by userfaultfd, either the process needs CAP_SYS_PTRACE, or this sysctl must be configured so that any unprivileged user can do it. In a typical implementation of a hypervisor with live migration (take QEMU/KVM as one such example), we do indeed need to be able to handle kernel faults. But, both options above are less than ideal: - Toggling the sysctl increases attack surface by allowing any unprivileged user to do it. - Granting the live migration process CAP_SYS_PTRACE gives it this ability, but *also* the ability to "observe and control the execution of another process [...], and examine and change [its] memory and registers" (from ptrace(2)). This isn't something we need or want to be able to do, so granting this permission violates the "principle of least privilege". This is all a long winded way to say: we want a more fine-grained way to grant access to userfaultfd, without granting other additional permissions at the same time. To achieve this, add a /dev/userfaultfd misc device. This device provides an alternative to the userfaultfd(2) syscall for the creation of new userfaultfds. The idea is, any userfaultfds created this way will be able to handle kernel faults, without the caller having any special capabilities. Access to this mechanism is instead restricted using e.g. standard filesystem permissions. Signed-off-by: Axel Rasmussen --- fs/userfaultfd.c | 76 ++++++++++++++++++++++++++------ include/uapi/linux/userfaultfd.h | 4 ++ 2 files changed, 66 insertions(+), 14 deletions(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index e943370107d0..8b92c1398169 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -30,6 +30,7 @@ #include #include #include +#include int sysctl_unprivileged_userfaultfd __read_mostly; @@ -413,13 +414,8 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason) if (ctx->features & UFFD_FEATURE_SIGBUS) goto out; - if ((vmf->flags & FAULT_FLAG_USER) == 0 && - ctx->flags & UFFD_USER_MODE_ONLY) { - printk_once(KERN_WARNING "uffd: Set unprivileged_userfaultfd " - "sysctl knob to 1 if kernel faults must be handled " - "without obtaining CAP_SYS_PTRACE capability\n"); + if (!(vmf->flags & FAULT_FLAG_USER) && (ctx->flags & UFFD_USER_MODE_ONLY)) goto out; - } /* * If it's already released don't get it. This avoids to loop @@ -2052,19 +2048,33 @@ static void init_once_userfaultfd_ctx(void *mem) seqcount_spinlock_init(&ctx->refile_seq, &ctx->fault_pending_wqh.lock); } -SYSCALL_DEFINE1(userfaultfd, int, flags) +static inline bool userfaultfd_allowed(bool is_syscall, int flags) +{ + bool kernel_faults = !(flags & UFFD_USER_MODE_ONLY); + bool allow_unprivileged = sysctl_unprivileged_userfaultfd; + + /* userfaultfd(2) access is controlled by sysctl + capability. */ + if (is_syscall && kernel_faults) { + if (!allow_unprivileged && !capable(CAP_SYS_PTRACE)) + return false; + } + + /* + * For /dev/userfaultfd, access is to be controlled using e.g. + * permissions on the device node. We assume this is correctly + * configured by userspace, so we simply allow access here. + */ + + return true; +} + +static int new_userfaultfd(bool is_syscall, int flags) { struct userfaultfd_ctx *ctx; int fd; - if (!sysctl_unprivileged_userfaultfd && - (flags & UFFD_USER_MODE_ONLY) == 0 && - !capable(CAP_SYS_PTRACE)) { - printk_once(KERN_WARNING "uffd: Set unprivileged_userfaultfd " - "sysctl knob to 1 if kernel faults must be handled " - "without obtaining CAP_SYS_PTRACE capability\n"); + if (!userfaultfd_allowed(is_syscall, flags)) return -EPERM; - } BUG_ON(!current->mm); @@ -2083,6 +2093,10 @@ SYSCALL_DEFINE1(userfaultfd, int, flags) refcount_set(&ctx->refcount, 1); ctx->flags = flags; ctx->features = 0; + /* + * If UFFD_USER_MODE_ONLY is not set, then userfaultfd_allowed() above + * decided that kernel faults were allowed and should be handled. + */ ctx->released = false; atomic_set(&ctx->mmap_changing, 0); ctx->mm = current->mm; @@ -2098,8 +2112,42 @@ SYSCALL_DEFINE1(userfaultfd, int, flags) return fd; } +SYSCALL_DEFINE1(userfaultfd, int, flags) +{ + return new_userfaultfd(true, flags); +} + +static int userfaultfd_dev_open(struct inode *inode, struct file *file) +{ + return 0; +} + +static long userfaultfd_dev_ioctl(struct file *file, unsigned int cmd, unsigned long flags) +{ + if (cmd != USERFAULTFD_IOC_NEW) + return -EINVAL; + + return new_userfaultfd(false, flags); +} + +static const struct file_operations userfaultfd_dev_fops = { + .open = userfaultfd_dev_open, + .unlocked_ioctl = userfaultfd_dev_ioctl, + .compat_ioctl = userfaultfd_dev_ioctl, + .owner = THIS_MODULE, + .llseek = noop_llseek, +}; + +static struct miscdevice userfaultfd_misc = { + .minor = MISC_DYNAMIC_MINOR, + .name = "userfaultfd", + .fops = &userfaultfd_dev_fops +}; + static int __init userfaultfd_init(void) { + WARN_ON(misc_register(&userfaultfd_misc)); + userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache", sizeof(struct userfaultfd_ctx), 0, diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h index 7d32b1e797fb..005e5e306266 100644 --- a/include/uapi/linux/userfaultfd.h +++ b/include/uapi/linux/userfaultfd.h @@ -12,6 +12,10 @@ #include +/* ioctls for /dev/userfaultfd */ +#define USERFAULTFD_IOC 0xAA +#define USERFAULTFD_IOC_NEW _IO(USERFAULTFD_IOC, 0x00) + /* * If the UFFDIO_API is upgraded someday, the UFFDIO_UNREGISTER and * UFFDIO_WAKE ioctls should be defined as _IOW and not as _IOR. In From patchwork Wed Jun 1 21:09:48 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Axel Rasmussen X-Patchwork-Id: 12867283 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A440BCCA47C for ; Wed, 1 Jun 2022 21:10:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231315AbiFAVK0 (ORCPT ); Wed, 1 Jun 2022 17:10:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54760 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231297AbiFAVKH (ORCPT ); Wed, 1 Jun 2022 17:10:07 -0400 Received: from mail-yw1-x114a.google.com (mail-yw1-x114a.google.com [IPv6:2607:f8b0:4864:20::114a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 53F48396BE for ; Wed, 1 Jun 2022 14:10:02 -0700 (PDT) Received: by mail-yw1-x114a.google.com with SMTP id 00721157ae682-30974094b5cso25508057b3.20 for ; Wed, 01 Jun 2022 14:10:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=GEuH7v2hm8gPbs+X2v5W8KutfNkKgsCF+/5mNPJwBK0=; b=NeP/OeNWbhVp3hYIumiRRFBaPXdgXyAjdD7Zj0iRpLOZr9GndhZskF8GFrI0+0V7jy UN8+h16HnW6rKS6i3HCFhE+iWsyJjtYRQW2in2IqUsCcb3Qwky5IW2whpRmS441F3S2C FxHMvZZe/UEWlqji0Ii/+wf3NDCs73ENyGUtGHUqrxfp0B7MbA8Omg4W5On4qYlsLGPy sp9/TGzUmEa5ZQIxOm6KVUET5G5/zTqvPFKuPvalDfVXTeP66q18+53RNjMKYeRRNw2I 3z58aWIWYSn4SGF4HorICFDufV7uC0oZ6W8Ws9D9zWp/n+KcdLIyLZuJb78wLY1gcDuL FsHA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=GEuH7v2hm8gPbs+X2v5W8KutfNkKgsCF+/5mNPJwBK0=; b=kSuw7eqYT0bGXBQdnt5NUxPB4Hv0oUuKOk2Yw0UfVOSTZ+VHs0Cd8xzi+OghTWbCe1 TXbTsVFbs3UELoBgTZA3SSq7T3zzyzBykXOEHEkZYl50kGwfR4uSHjeW0u8W6KveDV+h wBc2oBYBkI0PwyrhLFBwDAN0hXfYyspJrXqvcc0gUBEPjsuwJh8XT3J+yxr+vACXQJCE VL2gFZazWb0vOWEa2KJiw904fNKo54E0kNnWMqQmQxjU0LxwI9JiLG6LMbO8GmhHZTbg VHgTgOLbFIIA40pjnetUfrbQo8GtUgToMxNR5leD7rRcfJHrGumijVHBkd4VEe3qz1Fe lqYA== X-Gm-Message-State: AOAM5326wFOWgtpKtAe0bCbDAimAcsN4nsiUtepA1KDfKaGme57Kl8Oj EXmVJ0BmYq50310W3vBcjTO36Bk+uULNrIv3sYAq X-Google-Smtp-Source: ABdhPJxLYxJTU4wKWdQdJErOlnXgmFSzr5QQlaHudjQxgiYWQ/To+IWy0QKQkX1/fZdej8cYja73KHAsf5mUjbmiy+G7 X-Received: from ajr0.svl.corp.google.com ([2620:15c:2cd:203:aaec:e358:9f0e:2b26]) (user=axelrasmussen job=sendgmr) by 2002:a25:9ac1:0:b0:65c:bf5a:ce24 with SMTP id t1-20020a259ac1000000b0065cbf5ace24mr1913952ybo.378.1654117801445; Wed, 01 Jun 2022 14:10:01 -0700 (PDT) Date: Wed, 1 Jun 2022 14:09:48 -0700 In-Reply-To: <20220601210951.3916598-1-axelrasmussen@google.com> Message-Id: <20220601210951.3916598-4-axelrasmussen@google.com> Mime-Version: 1.0 References: <20220601210951.3916598-1-axelrasmussen@google.com> X-Mailer: git-send-email 2.36.1.255.ge46751e96f-goog Subject: [PATCH v3 3/6] userfaultfd: selftests: modify selftest to use /dev/userfaultfd From: Axel Rasmussen To: Alexander Viro , Andrew Morton , Charan Teja Reddy , Dave Hansen , "Dmitry V . Levin" , Gleb Fotengauer-Malinovskiy , Hugh Dickins , Jan Kara , Jonathan Corbet , Mel Gorman , Mike Kravetz , Mike Rapoport , Nadav Amit , Peter Xu , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , zhangyi Cc: Axel Rasmussen , linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org We clearly want to ensure both userfaultfd(2) and /dev/userfaultfd keep working into the future, so just run the test twice, using each interface. Signed-off-by: Axel Rasmussen --- tools/testing/selftests/vm/userfaultfd.c | 37 +++++++++++++++++++++--- 1 file changed, 33 insertions(+), 4 deletions(-) diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c index 0bdfc1955229..1badb5d31bf9 100644 --- a/tools/testing/selftests/vm/userfaultfd.c +++ b/tools/testing/selftests/vm/userfaultfd.c @@ -77,6 +77,9 @@ static int bounces; #define TEST_SHMEM 3 static int test_type; +/* test using /dev/userfaultfd, instead of userfaultfd(2) */ +static bool test_dev_userfaultfd; + /* exercise the test_uffdio_*_eexist every ALARM_INTERVAL_SECS */ #define ALARM_INTERVAL_SECS 10 static volatile bool test_uffdio_copy_eexist = true; @@ -154,12 +157,14 @@ static void usage(void) ret, __LINE__); \ } while (0) -#define err(fmt, ...) \ +#define errexit(exitcode, fmt, ...) \ do { \ _err(fmt, ##__VA_ARGS__); \ - exit(1); \ + exit(exitcode); \ } while (0) +#define err(fmt, ...) errexit(1, fmt, ##__VA_ARGS__) + static void uffd_stats_reset(struct uffd_stats *uffd_stats, unsigned long n_cpus) { @@ -383,13 +388,31 @@ static void assert_expected_ioctls_present(uint64_t mode, uint64_t ioctls) } } +static void __userfaultfd_open_dev(void) +{ + int fd; + + uffd = -1; + fd = open("/dev/userfaultfd", O_RDWR | O_CLOEXEC); + if (fd < 0) + return; + + uffd = ioctl(fd, USERFAULTFD_IOC_NEW, + O_CLOEXEC | O_NONBLOCK | UFFD_USER_MODE_ONLY); + close(fd); +} + static void userfaultfd_open(uint64_t *features) { struct uffdio_api uffdio_api; - uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK | UFFD_USER_MODE_ONLY); + if (test_dev_userfaultfd) + __userfaultfd_open_dev(); + else + uffd = syscall(__NR_userfaultfd, + O_CLOEXEC | O_NONBLOCK | UFFD_USER_MODE_ONLY); if (uffd < 0) - err("userfaultfd syscall not available in this kernel"); + errexit(KSFT_SKIP, "creating userfaultfd failed"); uffd_flags = fcntl(uffd, F_GETFD, NULL); uffdio_api.api = UFFD_API; @@ -1691,6 +1714,12 @@ int main(int argc, char **argv) } printf("nr_pages: %lu, nr_pages_per_cpu: %lu\n", nr_pages, nr_pages_per_cpu); + + test_dev_userfaultfd = false; + if (userfaultfd_stress()) + return 1; + + test_dev_userfaultfd = true; return userfaultfd_stress(); } From patchwork Wed Jun 1 21:09:49 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Axel Rasmussen X-Patchwork-Id: 12867279 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2EE0AC43334 for ; Wed, 1 Jun 2022 21:10:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231230AbiFAVKW (ORCPT ); Wed, 1 Jun 2022 17:10:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54578 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231312AbiFAVKK (ORCPT ); Wed, 1 Jun 2022 17:10:10 -0400 Received: from mail-yw1-x1149.google.com (mail-yw1-x1149.google.com [IPv6:2607:f8b0:4864:20::1149]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A55CA3982C for ; Wed, 1 Jun 2022 14:10:04 -0700 (PDT) Received: by mail-yw1-x1149.google.com with SMTP id 00721157ae682-30c2aa26ebfso25838227b3.4 for ; 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Wed, 01 Jun 2022 14:10:03 -0700 (PDT) Date: Wed, 1 Jun 2022 14:09:49 -0700 In-Reply-To: <20220601210951.3916598-1-axelrasmussen@google.com> Message-Id: <20220601210951.3916598-5-axelrasmussen@google.com> Mime-Version: 1.0 References: <20220601210951.3916598-1-axelrasmussen@google.com> X-Mailer: git-send-email 2.36.1.255.ge46751e96f-goog Subject: [PATCH v3 4/6] userfaultfd: update documentation to describe /dev/userfaultfd From: Axel Rasmussen To: Alexander Viro , Andrew Morton , Charan Teja Reddy , Dave Hansen , "Dmitry V . Levin" , Gleb Fotengauer-Malinovskiy , Hugh Dickins , Jan Kara , Jonathan Corbet , Mel Gorman , Mike Kravetz , Mike Rapoport , Nadav Amit , Peter Xu , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , zhangyi Cc: Axel Rasmussen , linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org Explain the different ways to create a new userfaultfd, and how access control works for each way. Signed-off-by: Axel Rasmussen --- Documentation/admin-guide/mm/userfaultfd.rst | 40 ++++++++++++++++++-- Documentation/admin-guide/sysctl/vm.rst | 3 ++ 2 files changed, 40 insertions(+), 3 deletions(-) diff --git a/Documentation/admin-guide/mm/userfaultfd.rst b/Documentation/admin-guide/mm/userfaultfd.rst index 6528036093e1..9bae1acd431f 100644 --- a/Documentation/admin-guide/mm/userfaultfd.rst +++ b/Documentation/admin-guide/mm/userfaultfd.rst @@ -17,7 +17,10 @@ of the ``PROT_NONE+SIGSEGV`` trick. Design ====== -Userfaults are delivered and resolved through the ``userfaultfd`` syscall. +Userspace creates a new userfaultfd, initializes it, and registers one or more +regions of virtual memory with it. Then, any page faults which occur within the +region(s) result in a message being delivered to the userfaultfd, notifying +userspace of the fault. The ``userfaultfd`` (aside from registering and unregistering virtual memory ranges) provides two primary functionalities: @@ -34,12 +37,11 @@ The real advantage of userfaults if compared to regular virtual memory management of mremap/mprotect is that the userfaults in all their operations never involve heavyweight structures like vmas (in fact the ``userfaultfd`` runtime load never takes the mmap_lock for writing). - Vmas are not suitable for page- (or hugepage) granular fault tracking when dealing with virtual address spaces that could span Terabytes. Too many vmas would be needed for that. -The ``userfaultfd`` once opened by invoking the syscall, can also be +The ``userfaultfd``, once created, can also be passed using unix domain sockets to a manager process, so the same manager process could handle the userfaults of a multitude of different processes without them being aware about what is going on @@ -50,6 +52,38 @@ is a corner case that would currently return ``-EBUSY``). API === +Creating a userfaultfd +---------------------- + +There are two ways to create a new userfaultfd, each of which provide ways to +restrict access to this functionality (since historically userfaultfds which +handle kernel page faults have been a useful tool for exploiting the kernel). + +The first way, supported by older kernels, is the userfaultfd(2) syscall. +Access to this is controlled in several ways: + +- By default, the userfaultfd will be able to handle kernel page faults. This + can be disabled by passing in UFFD_USER_MODE_ONLY. + +- If vm.unprivileged_userfaultfd is 0, then the caller must *either* have + CAP_SYS_PTRACE, or pass in UFFD_USER_MODE_ONLY. + +- If vm.unprivileged_userfaultfd is 1, then no particular privilege is needed to + use this syscall, even if UFFD_USER_MODE_ONLY is *not* set. + +The second way, added to the kernel more recently, is by opening and issuing a +USERFAULTFD_IOC_NEW ioctl to /dev/userfaultfd. This method yields equivalent +userfaultfds to the userfaultfd(2) syscall; its benefit is in how access to +creating userfaultfds is controlled. + +Access to /dev/userfaultfd is controlled via normal filesystem permissions +(user/group/mode for example), which gives fine grained access to userfaultfd +specifically, without also granting other unrelated privileges at the same time +(as e.g. granting CAP_SYS_PTRACE would do). + +Initializing up a userfaultfd +----------------------------- + When first opened the ``userfaultfd`` must be enabled invoking the ``UFFDIO_API`` ioctl specifying a ``uffdio_api.api`` value set to ``UFFD_API`` (or a later API version) which will specify the ``read/POLLIN`` protocol diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst index d7374a1e8ac9..e3a952d1fd35 100644 --- a/Documentation/admin-guide/sysctl/vm.rst +++ b/Documentation/admin-guide/sysctl/vm.rst @@ -927,6 +927,9 @@ calls without any restrictions. The default value is 0. +An alternative to this sysctl / the userfaultfd(2) syscall is to create +userfaultfds via /dev/userfaultfd. See +Documentation/admin-guide/mm/userfaultfd.rst. user_reserve_kbytes =================== From patchwork Wed Jun 1 21:09:50 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Axel Rasmussen X-Patchwork-Id: 12867282 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2B9ABCCA47A for ; Wed, 1 Jun 2022 21:10:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231185AbiFAVKZ (ORCPT ); Wed, 1 Jun 2022 17:10:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54686 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231317AbiFAVKK (ORCPT ); Wed, 1 Jun 2022 17:10:10 -0400 Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8E3CA25C47 for ; Wed, 1 Jun 2022 14:10:06 -0700 (PDT) Received: by mail-yb1-xb49.google.com with SMTP id 84-20020a250557000000b0065bb92955a2so2468152ybf.1 for ; Wed, 01 Jun 2022 14:10:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=dcDBeY/HLlNXef9d9FAHPxWe/EV2aZU1witDOt2KoeY=; b=KaDwHX79CJbASDMmgXRlKLc/huskW7utSclJ0kfppbnZS1T/syXXX0OOqqco2+9elP 5EBfVeZWFsTr/FQRRajBdxKDD8WMBg7o9fiYLOlSBVHnkUMU6qLlmQ8wbxRiy97vjj1n d1MHsEJH+Fi8Yb2ErPHvZ95O8Pno4nEVoSdAmNwSrCbw8KI+39rmeI321hQC0x1VXEWa VizEGAex47VEQ4UJzuGfcJgV8KzlCSFFPFdauODxm1cORxr0QYeWj8tzyU2u86tekVow Y2TOE/hImTDvfKNFRWfSNAw6WFb0njnagrXm1EE2xQotfnLtM0lz0f8/yYojMTbYOQce HPJQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=dcDBeY/HLlNXef9d9FAHPxWe/EV2aZU1witDOt2KoeY=; b=buOdHJg061vvb2EBnE9n5ekvVngYeAW+DzqayUaGSU2qChYjN8UEEnvNLY3Q8j4RUd q1BsPUOZrhFYe2b6WeXbo6GULLnd5tF2NA5FqROSHje6ASQQDvEwYqLPFlUFM8T4fcLX BCsHvZspaLIRg+pHwqEDR4B+yDbbPQc9ZQciz6+IF/i61kyrLvUJSv9iMKMmfNSvWR13 DteXY67ATTa1o5R94X1E1U309ai4RU3xXMfvRoDKjrIn+rLL6PchwY8N0k+ShKPOpmkY O6XViVjniYRpNUXazDnC4EcCscFjFXANLWpPBuSKdm9pZvZN6MDW4D/jAx8aQE/o7dr6 vbkw== X-Gm-Message-State: AOAM530Pkdj31Wf/w9YzXNZq6Erm0mQB31ORped7CuSLcOV6d1Gxo/Im dO94R1SOeFa2ICytQI+FopcaRvubA9n7MDGQ11NE X-Google-Smtp-Source: ABdhPJykmwhlBXZrVDl0pEafra93LcclZ+yr17pnesiatozzZ/fWqR+h2P6cAMloCLCsdJazTqo9524d106wb6pcRX79 X-Received: from ajr0.svl.corp.google.com ([2620:15c:2cd:203:aaec:e358:9f0e:2b26]) (user=axelrasmussen job=sendgmr) by 2002:a25:744:0:b0:64f:79e5:6528 with SMTP id 65-20020a250744000000b0064f79e56528mr1969376ybh.104.1654117805867; Wed, 01 Jun 2022 14:10:05 -0700 (PDT) Date: Wed, 1 Jun 2022 14:09:50 -0700 In-Reply-To: <20220601210951.3916598-1-axelrasmussen@google.com> Message-Id: <20220601210951.3916598-6-axelrasmussen@google.com> Mime-Version: 1.0 References: <20220601210951.3916598-1-axelrasmussen@google.com> X-Mailer: git-send-email 2.36.1.255.ge46751e96f-goog Subject: [PATCH v3 5/6] userfaultfd: selftests: make /dev/userfaultfd testing configurable From: Axel Rasmussen To: Alexander Viro , Andrew Morton , Charan Teja Reddy , Dave Hansen , "Dmitry V . Levin" , Gleb Fotengauer-Malinovskiy , Hugh Dickins , Jan Kara , Jonathan Corbet , Mel Gorman , Mike Kravetz , Mike Rapoport , Nadav Amit , Peter Xu , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , zhangyi Cc: Axel Rasmussen , linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org Instead of always testing both userfaultfd(2) and /dev/userfaultfd, let the user choose which to test. As with other test features, change the behavior based on a new command line flag. Introduce the idea of "test mods", which are generic (not specific to a test type) modifications to the behavior of the test. This is sort of borrowed from this RFC patch series [1], but simplified a bit. The benefit is, in "typical" configurations this test is somewhat slow (say, 30sec or something). Testing both clearly doubles it, so it may not always be desirable, as users are likely to use one or the other, but never both, in the "real world". [1]: https://patchwork.kernel.org/project/linux-mm/patch/20201129004548.1619714-14-namit@vmware.com/ Signed-off-by: Axel Rasmussen --- tools/testing/selftests/vm/userfaultfd.c | 41 +++++++++++++++++------- 1 file changed, 30 insertions(+), 11 deletions(-) diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c index 1badb5d31bf9..aeee6f1ad8ef 100644 --- a/tools/testing/selftests/vm/userfaultfd.c +++ b/tools/testing/selftests/vm/userfaultfd.c @@ -128,6 +128,8 @@ struct uffd_stats { const char *examples = "# Run anonymous memory test on 100MiB region with 99999 bounces:\n" "./userfaultfd anon 100 99999\n\n" + "# Run the same anonymous memory test, but using /dev/userfaultfd:\n" + "./userfaultfd anon:dev 100 99999\n\n" "# Run share memory test on 1GiB region with 99 bounces:\n" "./userfaultfd shmem 1000 99\n\n" "# Run hugetlb memory test on 256MiB region with 50 bounces:\n" @@ -144,6 +146,13 @@ static void usage(void) "[hugetlbfs_file]\n\n"); fprintf(stderr, "Supported : anon, hugetlb, " "hugetlb_shared, shmem\n\n"); + fprintf(stderr, "'Test mods' can be joined to the test type string with a ':'. " + "Supported mods:\n"); + fprintf(stderr, "\tdev - Use /dev/userfaultfd instead of userfaultfd(2)\n"); + fprintf(stderr, "\nExample test mod usage:\n"); + fprintf(stderr, "# Run anonymous memory test with /dev/userfaultfd:\n"); + fprintf(stderr, "./userfaultfd anon:dev 100 99999\n\n"); + fprintf(stderr, "Examples:\n\n"); fprintf(stderr, "%s", examples); exit(1); @@ -1607,8 +1616,6 @@ unsigned long default_huge_page_size(void) static void set_test_type(const char *type) { - uint64_t features = UFFD_API_FEATURES; - if (!strcmp(type, "anon")) { test_type = TEST_ANON; uffd_test_ops = &anon_uffd_test_ops; @@ -1626,10 +1633,28 @@ static void set_test_type(const char *type) test_type = TEST_SHMEM; uffd_test_ops = &shmem_uffd_test_ops; test_uffdio_minor = true; - } else { - err("Unknown test type: %s", type); + } +} + +static void parse_test_type_arg(const char *raw_type) +{ + char *buf = strdup(raw_type); + uint64_t features = UFFD_API_FEATURES; + + while (buf) { + const char *token = strsep(&buf, ":"); + + if (!test_type) + set_test_type(token); + else if (!strcmp(token, "dev")) + test_dev_userfaultfd = true; + else + err("unrecognized test mod '%s'", token); } + if (!test_type) + err("failed to parse test type argument: '%s'", raw_type); + if (test_type == TEST_HUGETLB) page_size = default_huge_page_size(); else @@ -1676,7 +1701,7 @@ int main(int argc, char **argv) err("failed to arm SIGALRM"); alarm(ALARM_INTERVAL_SECS); - set_test_type(argv[1]); + parse_test_type_arg(argv[1]); nr_cpus = sysconf(_SC_NPROCESSORS_ONLN); nr_pages_per_cpu = atol(argv[2]) * 1024*1024 / page_size / @@ -1714,12 +1739,6 @@ int main(int argc, char **argv) } printf("nr_pages: %lu, nr_pages_per_cpu: %lu\n", nr_pages, nr_pages_per_cpu); - - test_dev_userfaultfd = false; - if (userfaultfd_stress()) - return 1; - - test_dev_userfaultfd = true; return userfaultfd_stress(); } From patchwork Wed Jun 1 21:09:51 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Axel Rasmussen X-Patchwork-Id: 12867280 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DED43C433EF for ; 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Wed, 01 Jun 2022 14:10:08 -0700 (PDT) Date: Wed, 1 Jun 2022 14:09:51 -0700 In-Reply-To: <20220601210951.3916598-1-axelrasmussen@google.com> Message-Id: <20220601210951.3916598-7-axelrasmussen@google.com> Mime-Version: 1.0 References: <20220601210951.3916598-1-axelrasmussen@google.com> X-Mailer: git-send-email 2.36.1.255.ge46751e96f-goog Subject: [PATCH v3 6/6] selftests: vm: add /dev/userfaultfd test cases to run_vmtests.sh From: Axel Rasmussen To: Alexander Viro , Andrew Morton , Charan Teja Reddy , Dave Hansen , "Dmitry V . Levin" , Gleb Fotengauer-Malinovskiy , Hugh Dickins , Jan Kara , Jonathan Corbet , Mel Gorman , Mike Kravetz , Mike Rapoport , Nadav Amit , Peter Xu , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , zhangyi Cc: Axel Rasmussen , linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, Shuah Khan Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org This new mode was recently added to the userfaultfd selftest. We want to exercise both userfaultfd(2) as well as /dev/userfaultfd, so add both test cases to the script. Reviewed-by: Shuah Khan Signed-off-by: Axel Rasmussen Acked-by: Peter Xu --- tools/testing/selftests/vm/run_vmtests.sh | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/tools/testing/selftests/vm/run_vmtests.sh b/tools/testing/selftests/vm/run_vmtests.sh index 7e102246dd9f..930c54eb5b4b 100755 --- a/tools/testing/selftests/vm/run_vmtests.sh +++ b/tools/testing/selftests/vm/run_vmtests.sh @@ -121,12 +121,17 @@ run_test ./gup_test -a run_test ./gup_test -ct -F 0x1 0 19 0x1000 run_test ./userfaultfd anon 20 16 +run_test ./userfaultfd anon:dev 20 16 # Hugetlb tests require source and destination huge pages. Pass in half the # size ($half_ufd_size_MB), which is used for *each*. run_test ./userfaultfd hugetlb "$half_ufd_size_MB" 32 +run_test ./userfaultfd hugetlb:dev "$half_ufd_size_MB" 32 run_test ./userfaultfd hugetlb_shared "$half_ufd_size_MB" 32 "$mnt"/uffd-test rm -f "$mnt"/uffd-test +run_test ./userfaultfd hugetlb_shared:dev "$half_ufd_size_MB" 32 "$mnt"/uffd-test +rm -f "$mnt"/uffd-test run_test ./userfaultfd shmem 20 16 +run_test ./userfaultfd shmem:dev 20 16 #cleanup umount "$mnt"